1. Field of the Invention
This application relates to electronic indicating torque wrenches, and in particular, to a torque wrench that provides audible and visual indications when the desired torque is being applied.
2. Description of the Prior Art
Torque wrenches have found wide application in the tightening together of mechanical parts by means of nuts, bolts and bolt heads. Such wrenches are used to apply predetermined amounts of torque to the nuts and bolt heads for, as an example, precise securement of mating parts found typically in automobile engines and various other machines. Application of such predetermined torque values insures even stressing of the automotive and machine parts in order to minimize warping due to stress variances within the parts. Typically, known predetermined torque settings are required when mating parts, such as used to accommodate passage of fluids therebetween, are separated by compressible gasket seals. To prevent leakage between such parts, uniform compression of the gasket is required, thereby necessitating equal application of torque to the securing bolts.
Additionally, the bolts have mechanical stress limits which, if exceeded either cause their breakage or cause them to experience elongations beyond their yield point. If they are torqued beyond their yield point, loss of uniform stressing between the bolts can occur. Thus, it is important to know at exactly what torque level the bolts are being tightened.
Presently existing torque wrenches typically have an arm that connects a handle to a nut or bolt head engaging end. The nut or bolt head engaging end may have any of a number of configurations such as open end, box end or a socket. For application of torque, the nut or bolt head engaging end is placed over a nut or bolt head, and a torquing force is applied at the handle. Such devices usually have a pointer arm that traverses, upon application of a torquing force, a torque indicator dial located on the wrench handle. The devices are designed such that the user reads the torque indicating dial while he is applying torque to tighten a nut or bolt head. Thus, the user has an instantaneous reading of the applied torque, and can therefore terminate such torque application when it reaches a predetermined value.
In many situations, however, the awkward location of the nut or bolt head to be tightened is such that the physical orientation of the user prevents him from simultaneously applying the torque to the wrench while reading the indicator dial. In such situations, the user must reorient his body posture in order to read the dial, and therefore disturb the application of torque. Thus, the interruption of the torque application process for the purpose of reading the indicator dial, leads to mistorquing and therefore uneven stressing of the tightened bolts.
Such devices also suffer from flexure effects so that the applied torque results in the bending of the wrench arm causing a diminishing of the application of torque to the wrench handle and the bolt to be tightened. These flexure effects may result in mistorquing of the bolts.
The torque indicating dials on presently available devices are usually small and therefore, the small dial setting graduations do not facilitate accurate discrimination between closely valued torque settings, or to the identification of the desired torque value.
Additionally, the devices of the prior art thus far described couple the wrench arm to the nut or bolt head engaging end by means of a coupling spring. The amount of torque applied by the wrench is determined by the displacement of the spring, as read by a pointer arm that is coupled to the spring. Such devices, however, suffer from deterioration and fatigue with respect to time, and therefore there is a loss of accuracy and calibration after repeated usage.